Abstract: In this study, a lignin epoxy resin suitable for wood adhesive was synthesized in an aqueous phase by using lignin as raw material. To study the effect of reaction conditions of lignin epoxidation on the hydroxyl and epoxy groups of lignin-epoxy resin and the bonding strength of plywood, the structure of lignin-epoxy resin was characterized by FT-IR and 31P NMR, and the thermal stability of lignin-epoxy resin was analyzed by TG and DTG. The results showed that the epoxidation reaction mainly took place in the phenolic hydroxyl group. And in the process of epoxidation, the additional amount of NaOH exerted a greater effect on the structure of lignin epoxy resin and the bonding strength of plywood than that of epichlorohydrin. With the increase in the amount of NaOH added in the reaction process, the number of epoxy groups in lignin epoxy resin increased gradually and the bonding strength of plywood showed a trend of increasing firstly and then decreasing. When the molar ratio of a hydroxyl group to NaOH of lignin was 1:1, the bonding strength of plywood made of lignin epoxy resin can reach the maximum, and the wet strength can reach 1.61 MPa, which exceeded the requirements of class II board in Chinese national standard (≥0.7 MPa). SEM was used to study the bonding mechanism, it was found that the structure of cured lignin epoxy resin was more stable and compact when the degree of epoxidation was increased, which led to the improvement of the bonding strength of plywood. However, an excessively high degree of epoxidation will increase the particle size of the adhesive particles, resulting in the inability of the adhesive to form a good mechanical interlocking structure with the wood, thereby reducing the bonding strength of the plywood. Furthermore, the synthesis process of lignin epoxy resin wood adhesive was simplified, the epoxidized system can be directly applied to the wood adhesive, and after 30 days of storage, the bond strength did not decrease significantly. Besides, compared with commercial UF resin wood adhesive, the bonding strength of UF resin can reach the level of commercial UF resin. The results showed that this method may have a great application prospect in the wood adhesive industry.

Key words: lignin, lignin epoxy resin, wood adhesive, plywood, epoxy equivalent weight

摘要： 以木质素为原料，在水相中合成一种适用于木材胶黏剂的木质素环氧树脂。为了考察木质素环氧化反应条件对木质素环氧树脂的羟基和环氧基的影响，以及对胶合板的胶合强度的影响，采用FT-IR和31PNMR对木质素环氧树脂结构进行表征，并用TG和DTG对木质素环氧树脂的热稳定性进行分析。结果表明，环氧化反应主要发生在酚羟基上，在反应过程中，相比环氧氯丙烷，NaOH的加入量对木质素环氧树脂结构和胶合板的胶合强度影响更大。随NaOH加入量增加，木质素环氧树脂中环氧基团逐渐增多，胶合板的胶合强度呈现先升高、后降低的趋势。当木质素的羟基与NaOH摩尔比为1:1时，由木质素环氧树脂制得的胶合板胶合强度达到最大，湿强度达1.61 MPa，超过国家标准II类板的要求(≥0.7 MPa)。采用扫描电镜研究了黏接机理，发现环氧化程度提高时，固化后的木质素环氧树脂的结构更加稳定且致密，导致胶合板的胶合强度也提高。但过高的环氧化程度会增大胶黏剂的粒径，导致胶黏剂与木板不能形成更好的机械互锁结构，从而降低胶合板的胶合强度。还进一步简化了木质素环氧树脂木材胶黏剂的合成工艺，使环氧化反应后的体系无需处理即可直接应用于木材胶黏剂，减少了胶合板生产工艺流程。此外，经过30天的储存期，胶黏剂黏合强度没有明显下降。通过与商业脲醛树脂木材胶黏剂对比，其黏接强度可以达到商业脲醛树脂的水平。

关键词: 木质素, 木质素环氧树脂, 木材胶粘剂, 胶合板, 环氧当量